不存在行数据时返回零值

Question

我的问题之前已得到解决，但我似乎无法对我的查询应用任何解决方案以使其正常工作。非常感谢一些指导。

下面我当前的查询返回这个数据集：

  |  Age      |   Count   |
     0-1 day      300
     2-3 days     6000
     3-4 days     100 

SELECT(CASE WHEN time_dtm > SYSDATE -1 THEN '0-1 day'
        WHEN time_dtm > SYSDATE -2 AND time_dtm < SYSDATE -1 THEN '1-2 days'
        WHEN time_dtm > SYSDATE -3 AND time_dtm < SYSDATE -2 THEN '2-3 days'
        WHEN time_dtm > SYSDATE -4 AND time_dtm < SYSDATE -3 THEN '3-4 days'
        WHEN time_dtm > SYSDATE -5 AND time_dtm < SYSDATE -4 THEN 'Closed'
        END) AS Age, 
    COUNT( * ) AS "Count" 
FROM table_1 
WHERE id IN (1,2,3)
GROUP BY (CASE WHEN time_dtm > SYSDATE -1 THEN '0-1 day'
        WHEN time_dtm > SYSDATE -2 AND time_dtm < SYSDATE -1 THEN '1-2 days'
        WHEN time_dtm > SYSDATE -3 AND time_dtm < SYSDATE -2 THEN '2-3 days'
        WHEN time_dtm > SYSDATE -4 AND time_dtm < SYSDATE -3 THEN '3-4 days'
        WHEN time_dtm > SYSDATE -5 AND time_dtm < SYSDATE -4 THEN 'Closed'
        END)
ORDER BY (CASE WHEN time_dtm > SYSDATE -1 THEN '0-1 day'
        WHEN time_dtm > SYSDATE -2 AND time_dtm < SYSDATE -1 THEN '1-2 days'
        WHEN time_dtm > SYSDATE -3 AND time_dtm < SYSDATE -2 THEN '2-3 days'
        WHEN time_dtm > SYSDATE -4 AND time_dtm < SYSDATE -3 THEN '3-4 days'
        WHEN time_dtm > SYSDATE -5 AND time_dtm < SYSDATE -4 THEN 'Closed'
        END)

但是，我希望它像这样将零/空行显示为零：

  |  Age      |   Count   |
     0-1 day      300
     1-2 days     0
     2-3 days     6000
     3-4 days     100
     Closed       0

我已经阅读了过去几天的各种回复：NVL、COALESCE、FULL/LEFT/RIGHT OUTER JOIN、LEFT/RIGHT JOINS、UNION ALL 等等，这些都没有 CASE 语句，并试图自己解决它但！你必须知道什么时候停下来问路。

Answer 1

首先，重新编写您的查询。使用视图或公用表表达式来避免在 SELECT、GROUP BY、ORDER BY 子句中重复三次。您的查询变为：

WITH data AS (
    SELECT(CASE WHEN time_dtm > SYSDATE -1 THEN '0-1 day'
                WHEN time_dtm > SYSDATE -2 AND 
                     time_dtm < SYSDATE -1 THEN '1-2 days'
                WHEN time_dtm > SYSDATE -3 AND 
                     time_dtm < SYSDATE -2 THEN '2-3 days'
                WHEN time_dtm > SYSDATE -4 AND 
                     time_dtm < SYSDATE -3 THEN '3-4 days'
                WHEN time_dtm > SYSDATE -5 AND 
                     time_dtm < SYSDATE -4 THEN 'Closed'
           END) AS Age 
    FROM table_1 
    WHERE id IN (1,2,3)
)
SELECT Age, COUNT(*)
FROM data
GROUP BY Age
ORDER BY Age

然后，为了确保您想要的任何组都可以在结果中使用，您有很多选择。

你可以使用UNION ALL:

WITH data AS (
    SELECT(CASE WHEN time_dtm > SYSDATE -1 THEN '0-1 day'
                WHEN time_dtm > SYSDATE -2 AND 
                     time_dtm < SYSDATE -1 THEN '1-2 days'
                WHEN time_dtm > SYSDATE -3 AND 
                     time_dtm < SYSDATE -2 THEN '2-3 days'
                WHEN time_dtm > SYSDATE -4 AND 
                     time_dtm < SYSDATE -3 THEN '3-4 days'
                WHEN time_dtm > SYSDATE -5 AND 
                     time_dtm < SYSDATE -4 THEN 'Closed'
           END) AS Age 
    FROM table_1 
    WHERE id IN (1,2,3)

    -- The below will add one record for every desired Age group
    UNION ALL
    SELECT '0-1 day'  FROM DUAL UNION ALL
    SELECT '1-2 days' FROM DUAL UNION ALL
    SELECT '2-3 days' FROM DUAL UNION ALL
    SELECT '3-4 days' FROM DUAL UNION ALL
    SELECT 'Closed'   FROM DUAL
)
SELECT Age, COUNT(*) - 1 -- Subtract the extra record again
FROM data
GROUP BY Age
ORDER BY Age

一个完全不同的解决方案将涉及LEFT OUTER JOINs：

-- Groups is a dynamic table that contains the date ranges and their "Age" label
WITH groups AS (
    SELECT SYSDATE -1 lower, SYSDATE upper, '0-1 day'  Age FROM DUAL UNION ALL
    SELECT SYSDATE -2      , SYSDATE -1   , '1-2 days'     FROM DUAL UNION ALL
    SELECT SYSDATE -3      , SYSDATE -2   , '2-3 days'     FROM DUAL UNION ALL
    SELECT SYSDATE -4      , SYSDATE -3   , '3-4 days'     FROM DUAL UNION ALL
    SELECT SYSDATE -5      , SYSDATE -4   , 'Closed'       FROM DUAL
)
SELECT g.Age, NVL(SUM(t.counter), 0)
FROM groups g

-- LEFT OUTER JOINing "table_1" to "groups" will ensure that every group
-- appears at least once in the result
LEFT OUTER JOIN (
  SELECT 1 counter, t.* FROM table_1 t WHERE t.id IN (1,2,3)
) t
ON  t.time_dtm >= g.lower
AND t.time_dtm <  g.upper
GROUP BY g.Age
ORDER BY g.Age

在第二个示例中，您也可以不使用 CTE，并为 groups 表使用嵌套 SELECT。如果您的需求发生变化，很容易看出第二个示例在未来如何更简单地发展。